Touch-sensitive displays may be used as input devices in many different computing device environments. Generally, touch-sensitive displays comprise a mechanism for detecting the touch of a user's finger or other object on a display screen, and therefore allow a user to input selections or commands to a computing device by touching the display in an appropriate location indicated by a graphical user interface (GUI). A touch-sensitive display may detect touch via any of several different mechanisms, including but not limited to optical, capacitive, and resistive mechanisms.
To provide a richer and more intuitive user experience, some GUIs may be configured to alter an image displayed on the display screen in response to a user's touch to simulate a reaction to the touch. For example, some user-selectable items may appear on a GUI as buttons. Such buttons may be displayed in either a “button up” or “button pressed down” state to visually simulate the pressing of a button by the user. However, such graphical representations of a physical response to a touch input are generally binary in nature, having only two states (pressed or unpressed) that are presented to the user.